I N S U LAT I O N
FAC TS
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35
Comparing Fiber Glass
and Cellulose Insulation
Compare Today
Insulate and Save Tomorrow
Introduction
Before Choosing
Your Insulation
W
Things to consider when choosing an
insulation product include ease of application, thermal performance and value.
However, you should also consider the
overall lifetime performance of an insulation product as well as its related safety
aspects prior to purchase and installation.
hether your pocketbook
or the planet is your chief
concern, energy efficiency
can add up to a lot of savings.
Reducing energy demand
reduces the amount of fossil fuel
combustion needed to heat and
cool homes, which in turn
decreases the amount of carbon
dioxide emitted into the atmosphere. In terms of your pocketbook, reducing your energy consumption means lower utility bills.
While there are many things you
can do to increase your home’s
energy efficiency, one of the most
inexpensive ways is to install additional insulation.
www.naima.org
A Side by Side
Comparison
One way to compare insulation products is to do a side by side comparison.
Here we compare the two most common
types of insulation: fiber glass and cellulose. The following comparison reveals
important differences between the two
products which you should consider
before making a final decision.
Thermal
Resistance
Air Infiltration
Water Vapor
Sorption
Resistance to
Corrosion
Convection
Use of Recycled
Materials
Impact of
Weight
Sound Control
Fire Safety
Safety
Settling & Loss
of R-Value
THERMAL RESISTANCE R-VALUE
T
he thermal resistance of insulation
is designated by R-value. R-value is
resistance to heat flow - the higher the
R-value, the greater the insulating
power. Thickness of insulation is only
one factor that determines its R-value.
To ensure that consumers are provided
with accurate information regarding
R-values, the Federal Trade Commission
(FTC) in 1980 established a rule which
mandates that specific R-value information for home
insulation
products be
disclosed in
certain ads
and at the
point of sale.
The purpose
of the FTC R-value disclosure requirement for advertising is to prevent consumers from being mislead by certain
claims which have a bearing on insulating value. When insulating a home,
it’s important that the homeowner gets
the R-value specified and that the thermal performance lasts over time.
Fiber Glass Insulation
The R-value per inch of fiber glass
insulation can vary depending on the
density. Fiber glass batts and rolls, both
faced and unfaced, have R-values printed
on them. Standard fiber glass batt insulation has an R-value per inch of approximately 3.0. Most fiber glass manufacturers offer high-performance insulation
products that yield a higher R-value per
inch (4.0+). However, in nearly all applications, the overall R-value specified is
what counts, not the R-value per inch.
It’s also very important that the R-value
does not deteriorate. The R-value of fiber
glass does not deteriorate over time.
Cellulose Insulation
Cellulose insulation manufacturers
promote the product’s “higher R-value
per inch” as making it a better value than
fiber glass. Higher R-value per inch is not
important in selecting insulation material.
It is an advantage only in areas with little
space for insulation. In those particular
applications, fiber glass high density insulation (R-13 and R-15 batts) provides
higher R-value per inch than cellulose.1
SETTLING AND LOSS OF R-VALUE
S
ettling is an important consideration in insulation product selection
as it directly
relates to
the installed
thermal performance
over time.
Fiber Glass Insulation
Cellulose Insulation
Properly installed fiber glass batts and
rolls do not settle. Some fiber glass
loose-fill insulation may settle over time
(usually around 1 percent). This settling
does not alter the thermal performance
of fiber glass insulation.
When manufacturers’ installation procedures are employed, fiber glass insulation maintains its thermal performance
for the life of the building.
Cellulose manufacturers agree that
their products settle over time.2 Most set
the settling rate at about 20%. Therefore,
if cellulose is mistakenly installed to its
labeled settled thickness, it may lose
about 20% of its R-value when it settles.
When the product is not labeled for
installed thickness, the Insulation Contractors Association of America (ICAA)
recommends that an additional 25% of
thickness be added above the labeled settled thickness.
If exposed to moisture, it will not wick
up and hold water, thus it resists any permanent loss of R-value. If fiber glass insulation becomes saturated as the result of
flooding or other events not related to
actual product use, it should be removed
and replaced.
nently reduced. Assuming existing cellulose does dry after becoming wet, there
is a concern that the fire retardant chemicals may “wash away” leaving insulation
materials insufficiently protected. In
addition, studies conducted in Canada,
New England and Ohio demonstrated
that wet-spray applications of cellulose
insulation do not achieve their advertised
R-value until dry and may take as long as
two months to dry.3 In many cases, wetspray applications may need to remain
uncovered until completely dry.
WATER VAPOR SORPTION
I
n general, insulation will lose R–value
when wet. However, there are important differences in the water vapor
sorption properties of the two insulations which can impact their installed
performance.
Fiber Glass
Insulation
Cellulose Insulation
Insulation
made of fiber
glass is not
absorbent.
Cellulose insulation is made of shredded newspaper and will absorb moisture.
Also, if soaked, cellulose will “mat” down
and thermal performance can be perma-
2
CONVECTION
C
onvection is a form of heat flow in
which heat is transmitted by air
currents. When air is heated, it
expands, becomes less dense and moves
in an upward direction. Generally,
convection has
no effect on
insulation performance.
Fiber Glass Insulation
Cellulose Insulation
Fiber glass batts and rolls are not
affected by convection. However, some
lighter density loose-fill fiber glass may
be affected slightly in limited applications such as those found in extremely
cold weather environments. Laboratory
attic tests have shown that loose-fill products experience improved thermal performance as the temperature in an attic
drops, but that some light density loosefill products then may see a reduction in
thermal performance as attic temperatures drop further.
Convection will not affect the thermal performance of cellulose due to its
heavy density.
Fiber Glass Insulation
Cellulose Insulation
Fiber glass insulation is extremely
thermally efficient, yet light in weight.
Homeowners can install fiber glass insulation up to R-70 over 1/2″ ceiling drywall with framing spaced 24″ on centers
without causing drywall sag.
Based on U.S. Gypsum weight limit
recommendations for backloaded standard
drywall* and the installed density of shredded newspaper insulations, there is potential for ceiling drywall to sag at R-values
above R-30 for regular cellulose insulation
when installed over 1/2″ ceiling drywall
with framing spaced 24″ on centers.
THE IMPACT OF WEIGHT
W
hen installing insulation above
ceilings, homeowners should take
into consideration the impact that the
insulation weight can have on the ceiling structure of the home. The impact
of weight is
primarily an
issue in northern climates
where R-values
of 30 and
higher are commonplace.
* Gypsum Construction Handbook, 1992 edition, pages 28 and 102
FIRE SAFETY
F
ire resistance is an important
attribute of any insulation material.
It is in a
homeowner’s
best interest to
consider the
flame-resistance properties of the
insulation in
his or her
home. In terms of fire safety, fiber glass
and cellulose perform quite differently.
Fiber Glass Insulation
Cellulose Insulation
Fiber glass insulation is made from
sand and other inorganic materials which
are melted and then spun into fiber glass.
Fiber glass is naturally noncombustible
and remains so for the life of the product. It requires no additional fire-retardant chemical treatments. Unfaced fiber
glass insulation also is recognized by
building code groups as an acceptable
fire stop in residential wood frame walls.
Most kraft and foil facings available
on some fiber glass insulation are themselves combustible. Products with such
facings are intended for non-exposed
applications and should not be left
exposed. When properly installed, these
products do not pose a fire hazard.
Cellulose insulation is made of groundup or shredded newspaper which is naturally combustible. In fact, cellulose insulation is regulated as a recognized fire hazard
by the Consumer Product Safety Council
(CPSC).4 To protect against fire hazards, cellulose insulation is heavily treated with fire
retardant chemicals prior to installation.
Tests conducted by the California
Bureau of Home Furnishings and Thermal
Insulation have demonstrated that some cellulose samples failed the standard fire safety
test only six months after installation.5
Additionally, smoldering combustion and
re-ignition problems are concerns with cellulose insulation should a fire start.6 Even
properly treated cellulose insulations will
burn at about 450°F. That’s the surface
temperature of a 75 watt light bulb.7
3
RESISTANCE TO CORROSION
I
t makes sense
to avoid the
use of products
that may cause
corrosion problems in a home.
Fiber Glass Insulation
Cellulose Insulation
Fiber glass insulation is not corrosive
and contains no chemicals that can corrode pipes and wires.
Certain chemicals routinely applied
as a fire retardant to most cellulose insulation (particularly the sulfates) can cause
the corrosion of pipes and wires under
some conditions.8
package, and not the insulation
installed in the wall cavity.
A 1997 study conducted by the
National Association of Home Builders
(NAHB) Research Center for the U.S.
Environmental Protection Agency’s
Energy Star Homes Program9 could find
no relationship between the type of insulation used and the amount of air infiltration. The study
determined that
the individual air
sealing practices
of the insulators
had a larger
impact on air
leakage than the
insulation products themselves. These
findings were confirmed by a 1997 study
conducted by a researcher at Penn State
University10 and a 1996 study by a St.
Louis, MO utility company.11
Fiber Glass Insulation
AIR INFILTRATION
A
ir infiltration is the uncontrolled
leakage of air into and out of a
home. It is driven by wind, temperature differences, or HVAC applianceinduced pressures.
If a wall cavity has been properly
closed off using drywall, sheathing, and
caulking, very little air will flow through a
wall cavity regardless of the type of insulation used. Openings for wiring runs, light
switches and electrical outlets where air
infiltration can occur, can be sealed with
foam sealants, caulking or foam gaskets.
To control air leakage in a home, a housewrap or other air infiltration control
strategies should be considered to limit air
infiltration through cracks and joints.
Recently, there has been some
debate over which insulation products
are better at reducing air infiltration.
The fact is, research shows that air infiltration is dependent on the sealant
Properly installed fiber glass insulation in a wall cavity matches cellulose in
combating heat loss from air infiltration.
Minimizing air infiltration is dependent
on the sealant package, not the insulation. The purpose of insulation is to provide thermal performance.
Cellulose Insulation
Despite claims that wet-spray cellulose
eliminates air infiltration, the research
shows that what’s in the cavity of the wall
or attic - fiber glass or cellulose - has little,
if any, effect on air infiltration.12
SOUND CONTROL
I
n general, the density of the insulation
material in a sidewall assembly has little, if any, effect on the Sound Transmission Class (STC) rating of the assembly.
STC ratings are a measure of the effectiveness of a given partition construction
in reducing airborne sound transmission. Insulation thickness, however, has
a more significant effect on STC ratings
than does density. In comparison testing,
representative 2 x 4 and 2 x 6 wood stud
and metal stud walls demonstrated
equivalent or slightly better performance
for fiber glass over cellulose when the
cavities were completely filled.13
Fiber glass Insulation
Cellulose Insulation
Fiber glass insulation significantly
reduces sound transmission in wall, ceiling and floor assemblies. The first inch of
fiber glass insulation can increase the STC
value by 3 or 4 points in some constructions. Each additional inch of fiber glass
insulation increases the STC value from
one to two points. (Refer to NAIMA publication BI405 - Sound Control for Commercial and Residential Buildings)
Cellulose insulation is also considered
a good insulator against unwanted sound
in wall and ceiling assemblies.
4
USE OF RECYCLED MATERIALS
I
ncreased attention has been given to
recycling and recycled products as
concerns about our environment have
heightened. Both fiber glass and cellulose manufacturers use a significant
amount of
recycled
materials in
the manufacture and packaging of their
products.
Fiber Glass Insulation
Cellulose Insulation
Between 1992 and 2000, the fiber
glass insulation industry recycled approximately 8,355,848,000 lbs. of pre- and
post-consumer glass containers, eliminating the need for millions of cubic feet of
landfill space.
Many fiber glass insulation manufacturers have plants that use up to 40% or
more recycled materials in their products.
The current industry average is 30% recycled content. Manufacturers are currently exploring ways in which their use
of recycled materials can be increased
without compromising the effectiveness
of their insulation products when
installed in attics, sidewalls and floors.
In addition, the packaging materials
used by fiber glass manufacturers can
be recycled.
Cellulose insulation is generally made
up of about 80% recycled newspapers and
20% fire-retardant chemicals. On the surface, cellulose insulation may appear to be
the more environmentally acceptable
insulation choice as it is made from shredded newspaper. However, it takes three
times more cellulose material by weight
than fiber glass to insulate a typical home.
In addition, an average 1200 square foot
attic insulated to R-38 with cellulose insulation would introduce 300 pounds of fire
retardant chemicals into the home.
Fiber Glass Insulation
Cellulose Insulation
Fiber glass insulation is one of the
most thoroughly tested building materials in use today. The great amount of
medical scientific evidence compiled
over more than fifty years by industry,
government and independent research
organizations supports the conclusion
that fiber glass insulation is safe to use
when manufacturers’ recommended
work practices are followed.
Questions about the health and safety
aspects of cellulose insulation persist in
the building industry because comprehensive medical scientific testing of the products has never been conducted. Repeated
requests by union and contractor groups
that such testing be undertaken have been
ignored.14 Given the high levels of exposure measured during cellulose installation, only after long-term experiments are
available will it be known if cellulose insulation is safe to use.
SAFETY
T
he value of scientific research
regarding the health aspects of insulation materials cannot be overstated
in relation to
the safety of
workers and
the public.
5
REFERENCES
1.
2.
ASHRAE Fundamentals Handbook, 1997
Facts #30, Insulation and Fire Safety,
MO. William Conroy, Division Marketing
The North American Insulation Manufactur-
Arizona ICAA Chapter Request, Insulation
ers Association (NAIMA).
12.
Ibid.
Corrosiveness Testing of Thermal Insula-
13.
National Research Council of Canada
Contractors Monthly (May 1995).
3.
7.
(pps.24.4-24.5).
8.
“Wet-Spray Cellulose - Questions About
tion Materials - A Simulated Field Exposure
Drying,” Energy Design Update, July 1989
Study Using a Test Wall, Report ORNL/Sug.
Edition, p.1. “Effect of Wet-spray Cellulose
78-7556/4, September 1988.
on Walls,” Energy Design Update, October
Report, “Gypsum Board Walls: Transmission Loss Data.” March 1998, #761.
14.
Arizona ICAA Chapter Request, Insulation
Field Demonstration of Alternative Wall
Contractors Monthly (May 1995), and Let-
1989, p.3.
Insulation Products. Prepared for the U.S.
ter to TSCA Public Docket Office from the
4.
16 C.F.R. Part 1209.
Environmental Protection Agency by NAHB
Laborers’ Health and Safety Fund of North
5.
California Bureau of Home Furnishings and
Research Center, Inc., November 1997.
America (September 23, 1991).
Thermal Insulation, Long-Term Aging Stud-
6.
9.
Supervisor, 1995.
10.
A Field Study of the Effect of Insulation
ies on Loose-fill Cellulose Insulation: Part
Types on the Air Tightness of Houses.
IV 7V (1991).
G.K. Yuill, Ph.D, Pennsylvania State
Letter to Dale Lewis from Lewis County
University Department of Architectural
(Washington State) Public Utility District,
March 20, 1991.
Engineering, 1996.
11.
Research and Development Project,
“Maple Acres,” Union Electric, St. Louis,
ABOUT NAIMA
NAIMA is the association for North
American manufacturers of fiber glass,
rock wool, and slag wool insulation
products. Its role is to promote energy
efficiency and environmental preservation through the use of fiber glass, rock
wool, and slag wool insulation, and to
encourage the safe production and use
of these materials.
For more information, contact:
NAIMA
44 Canal Center Plaza, Suite 310
Alexandria, VA 22314
Tel: 703/684-0084
Fax: 703/684-0427
E-mail: [email protected]
Website: http://www.naima.org
NAIMA BUILDING INSULATION
COMMITTEE MEMBERS:
CertainTeed Corporation
PO Box 860
Valley Forge, PA 19482
800/233-8990
Johns Manville
PO Box 5108
Denver, CO 80217-5108
800/654-3103
Knauf Fiber Glass
One Knauf Drive
Shelbyville, IN 46176
800/825-4434
Owens Corning
One Owens Corning Parkway
Toledo, OH 43659
800/GET-PINK
PUB. NO. BI475 3/02